The overall objective of our research is to understand the course of differentiation of erythroid cells in terms of membrane glycoproteins and evaluate cell membrane glycoproteins as onco-differentiation cell surface markers, shared by tumor cells and normal cells at an early stage of differentiation. We are dealing with two major aspects. First, we are testing whether certain membrane glycoproteins can function as tumor-specific markers as well as normal immature cells. We have analyzed cell surface glycoproteins of newly isolated human erythroleukemic cells (HEL) and found that some cell surface glycoproteins (Gp105, Gp95) are expressed on these cells and K562 cells as well as normal immature cells but not on mature erythrocytes. Studies are in progress to isolate Gp105 and look at the distribution of Gp105 in stem cell differentiation in normal and leukemic conditions. Secondly, we are clarifying structure change of lactosaminoglycan throughout the various ontogenic and oncogenic stages. We have found that lactosaminoglycan displays a drastic structural change during ontogenesis and differentiation. Further studies will be to complete elucidation of the structures of lactosaminoglycan from both fetal and adult erythrocytes. Studies will be helped by using new instrumental analysis including fast atom bombardment mass spectrometry. In addition, the carbohydrate structure of Gp105, specifically present in leukemic cells and immature normal cells, will be characterized.